"We intend to vigorously defend the rights of our patients and the citizens of Berkeley to be able to obtain medical cannabis from a responsible, licensed dispensary," said Sean Luse, the chief operating officer of the Berkeley Patients Group.

The lawsuit was filed in federal court in San Francisco last Thursday by U.S. Attorney Melinda Haag, the chief federal prosecutor for Northern California.

It asks the court to order the forfeiture from the group's landlord of the group's leased storefront at 2366 San Pablo Ave., on the grounds that the property is used for illegal sales of marijuana.

The Berkeley Patients Group, founded in 1999, is the oldest continuously operating medical marijuana dispensary in the Bay Area and serves more than 10,000 patients, Luse said.

The forfeiture lawsuit is part of a crackdown announced by Haag and the other three regional U.S. attorneys in California in 2011. The prosecutors said they planned to target dispensaries they considered to be large-scale commercial operations by filing forfeiture lawsuits against landlords.

Kris Hermes, a spokesman for Americans for Safe Access, an Oakland-based marijuana advocacy group, said the new case is one of about 20 currently active forfeiture lawsuits against California dispensaries.

But Hermes said at least several hundred other medical marijuana stores in California have closed since 2011 because of threats of such lawsuits.

Another of the pending lawsuits is one filed last year against Harborside Health Center in Oakland, the state's largest dispensary.

The state's voter-approved Compassionate Use Act of 1996, also known as Proposition 215, protects seriously ill patients who have a doctor's recommendation from being prosecuted under state law for using marijuana as medicine.

But federal laws criminalizing marijuana make no exception for state medical marijuana laws.

The new lawsuit was assigned to U.S. Magistrate Nathaniel Cousins of San Francisco and is scheduled for a status conference on July 31.

Luse said the dispensary will keep operating while the case is ongoing.

Henry Wykowski, a lawyer for the Berkeley Patients Group, said the forfeiture effort "places the patients in unnecessary danger by forcing them to obtain their medicine from gangs and cartels."

In announcing the crackdown in 2011, Haag said Northern California prosecutors would begin by targeting dispensaries near schools and parks, but wouldn't necessarily be limited to such sites.

"None are immune from action by the federal government," Haag said at the time.

After receiving a letter from Haag threatening forfeiture in 2011, the Berkeley Patients Group moved to its present location from a previous address that was within 1,000 feet of a private elementary school.

Haag's May 2 lawsuit asserts that the group's current location is within 1,000 feet of two preschools.

Wykowski said today that before moving, the group received a letter from the city of Berkeley stating that the new address was an "appropriate location."

Luse said that four City Council members and Mayor Tom Bates attended a noon press conference to support the dispensary today.